Kinetics of the photosynthetic pigments chlorophyll a (A), chlorophyll b (B), and carotenoids (C) in Pisum sativum L. treated with various PbCl2 concentrations for different time (2, 5, 7, and 10 days). Results are calculated as a percent of the control. Data are presented as mean ± SEM from at least three independent experiments. Asterisks represent statistical significance between the control and the treated samples (*** P < 0.001). Where no error bars are evident, they are equal to, or smaller than. the values.